Antenna

ABSTRACT

An antenna comprises at least two or more radiators such as, especially dual-polarized radiators, and at least one additional passive conducting decoupling elements. The decoupling element, in its longest direction of extension, or at least one component of the decoupling element, with its longest direction of extension, extends in the propagation direction of the electromagnetic waves and/or perpendicular to the plane of the reflector.

This application is the US national phase of international applicationPCT/GB00/06411, filed Jun. 7, 2000, which designated the US.

The invention relates to an antenna having at least two fed radiatingelements as claimed in the precharacterizing clause of claim 1.

As is known, in the case of antennas having at least two fed radiatingelements, that is to say having a number of fed radiating elements, itis important to achieve as much decoupling as possible between thedifferent radiating elements. Particularly in the case of dual-polarizedradiating elements or arrays, a high level of decoupling is desirablebetween the radiating elements for one polarization and the radiatingelements for the other polarization, which is at right angles to it.Such arrays may comprise, for example, a number of elements in the formof dipoles, slots or planar radiating elements, such as those which areknown, for example, from EP 0 685 900 A1 or from the prior publication“Antennen” [Antennas], Part 2, Bibliographical Institute inMannheim/Vienna/Zurich, 1970, pages 47 to 50. This document describes,for example, omnidirectional radiating elements with horizontalpolarization in the form of a dipole square or a cruciform dipole, inwhich coupling exists between the two systems which are physicallyoffset through 90°.

In order to increase the directionality, such radiating elements arenormally arranged in front of a reflector. A disadvantage that has beenfound in this case is that the intrinsically good decoupling inparticular between radiating elements with orthogonal polarizations ismade worse by arranging them as an array, in particular due to theinfluences of the reflector.

appropriate decoupling elements have already been proposed in order tocompensate for these disadvantages mentioned above.

The previously published DE 196 27 015 A1 has already proposed thatdecoupling devices in the form of strips or crosses be arranged betweenthe radiating elements, in which case, particularly when using strips,these strips are arranged along the connecting line of two antennadevices, which are arranged offset with respect to one another, in anantenna array. In contrast to already known solutions relating to this,these strips are not arranged transversely with respect to theconnection direction between two antenna arrangements, but parallel tothe connecting line between two adjacent antenna devices.

The previously published DE 198 21 223 A1 proposes that passive striparrangements be used as decoupling elements, which are provided suchthat they are aligned running centrally between in each case two antennadevices, which are arranged offset like an antenna array, between theseantenna devices in the transverse direction with respect to thedirection in which the radiating elements are fitted, or else arearranged parallel to the direction in which the radiating elements arefitted, and to the side of said radiating elements at the same time. Tothis extent, this arrangement corresponds to that already proposed inthe previously published U.S. Pat. No. 3,541,559, which likewiseproposes that the individual decoupling elements be arranged to the sideof the individual antennas, like a frame.

Furthermore, GB 2 171 257 A discloses an antenna array which has anumber of dipoles arranged vertically one above the other, with aprojecting element in each case being arranged above two dipoles whichare arranged one above the other, with the aim of improving thedecoupling between the dipoles. This antenna array, which is alreadyknown from this document, is, in fact, constructed using striplinetechnology.

The object of the present invention, in the case of antennas having atleast two fed radiating elements, in particular in the case of antennaarrays and at the same time in particular in the case of dual-polarizedantenna arrays, is to allow a further improved capability for decouplingbetween the various radiating elements.

According to the invention, the object is achieved by the featuresspecified in claim 1.

Advantageous refinements of the invention are specified in the dependentclaims.

It must be regarded as being extremely surprising that, in completecontrast to all the previously published prior art, it is now proposedthat conductive decoupling elements be used, with their main extentdirection, that is to say with their longest extent in the propagationdirection of the electromagnetic wave and/or with their longest extent,being aligned at right angles to a reflector. In this case, thealignment need not correspond exactly to the propagation direction ofthe electromagnetic wave, and do not correspond exactly to theperpendicular to the plane of a reflector. All that is necessaryaccording to the invention is for the decoupling elements, which arepreferably in the form of rods, to be aligned with a component in thepropagation direction of the electromagnetic waves, that is to say inparticular running at right angles to the plane of the reflector plate,with at least these components representing a greater value than acomponent at right angles thereto. If the decoupling elements areconfigured in the form of rods, this means, in other words, that theangle between the longitudinal extent of the decoupling elements and aperpendicular to the reflector plate plane (that is to say to thepropagation direction of the electromagnetic waves) is less than 45°.

The system according to the invention—and this is particularlysurprising—has critically significant advantages particularly in thecase of dual-polarized antennas, which hence comprise, in particular, atleast one cruciform dipole or at least one dipole square. In contrast,the coupling elements which are known from GB 2 171 257 A relate only toa dipole arrangement with one polarization, which are also adjacent.

Thus, according to the invention, two mutually perpendicularpolarizations are preferably in each case affected, in which noradiating elements located vertically alongside one another, and whichcould be decoupled, are provided. A further difference to the prior artis that, in the case of dual-polarized antennas, two separate inputs areused, between which the decoupling (or isolation) must be measurable,while, in the case of the improved decoupling with a deeper arrangementwith only one polarization, such decoupling is not measurable (as, infact, there is only one input).

As mentioned, the decoupling elements according to the invention arepreferably in the form of rods and/or pins.

The decoupling elements according to the invention can in this case bearranged, for example, between two radiating elements, for examplebetween two or more vertically polarized or horizontally polarizedradiating elements, in each case in the region of the connecting linebetween these radiating elements.

In the case of cruciform dipoles, for example, the decoupling elementsaccording to the invention, which are preferably seated perpendicular onthe reflector plate, can be arranged in the immediate area between theindividual dipole halves, for example, in plan view, on an anglebisector of a cruciform dipole arrangement.

One or more of the decoupling elements according to the invention canlikewise, for example in the case of a dipole square, be arranged withinthe dipole square, and in this case once again preferably on an anglebisector of the dipole square.

The decoupling elements, which are in the form of rods according to theinvention, extend as stated with their greatest longitudinal extent orcomponent in the propagation direction of the magnetic waves and/or atright angles to the reflector plane. In this case, the decouplingelements may have a uniform cross section or widely differingcross-sectional shapes, for example with a round cross section or with aregular cross section or an irregular n-polygonal, for example square orhexagonal cross section, etc.

However, the cross section may in this case also vary over the length ofthe decoupling elements according to the invention. It is likewisepossible for the cross-sectional areas not to be rotationallysymmetrical but, for example, to have different longitudinal extentsalong two mutually perpendicular section axes running parallel to thereflector surface.

Finally, it is also possible for the decoupling elements according tothe invention also to be provided, in particular at their end oppositethe reflector plate, with formed-out regions or fixtures, which may alsoextend transversely with respect to the vertical extent component of thedecoupling element, and hence transversely with respect to thepropagation direction of the electromagnetic waves and/or parallel tothe plane of the reflector plate.

The invention will be explained in more detail in the following textwith reference to exemplary embodiments. In this case, in detail:

FIG. 1a shows a schematic plan view of two dipoles, which are arrangedoffset with respect to one another in the vertical fitting direction,and with a decoupling element according to the invention seated betweenthem.

FIG. 1b shows a schematic side view of the exemplary embodiment shown inFIG. 1a, along the arrow 2 in FIG. 1;

FIG. 2 shows a plan view of a modified exemplary embodiment of anantenna;

FIG. 3 shows a further modified exemplary embodiment of the invention,based on a cruciform dipole;

FIG. 3a shows a perspective illustration of the exemplary embodimentshown in FIG. 3;

FIG. 3b shows a plan view of the exemplary embodiment shown in FIG. 3;

FIG. 3c shows a schematic side view of the exemplary embodiment shown inFIGS. 3 to 3 b, along the arrow 2 in FIG. 3,

FIG. 4 shows a modified exemplary embodiment of the invention, for thecase of a dipole square;

FIG. 5 shows an antenna according to the invention having two cruciformdipoles arranged offset with respect to one another;

FIG. 6 shows a further exemplary embodiment of the invention, based ontwo dipole squares arranged offset with respect to one another;

FIGS. 7 to 10 show different side views of different embodiments of adecoupling element.

The following text refers to FIGS. 1a and 1 b which show, in a schematicplan view, an antenna 1 having at least two radiating elements 3, namelycomposed of two dipole radiating elements 3 a, each having two dipolehalves 13′, which, according to the exemplary embodiment shown in FIG.1, are arranged at an appropriate suitable distance in front of areflector 5 or a reflector plate 5. The schematic side view illustratedin FIG. 1b shows the respectively associated balancing elements 7, viawhich the dipole halves 13′ are held with respect to the reflector plate5.

The dipole radiating elements 3 a are arranged, with their dipole halves13′, offset with respect to one another on a fitting line 11 in theillustrated exemplary embodiment.

A decoupling element 17 according to the invention is arranged betweenthe two radiating elements 3, parallel to the propagation direction ofthe electromagnetic wave (that is to say, if the far field isconsidered, at right angles to the plane under consideration or theplane of the drawing), that is to say at the same time also at rightangles to the plane of the reflector 5, in the illustrated exemplaryembodiment and, in the illustrated exemplary embodiment, this decouplingelement 17 comprises a decoupling element 17 a which is in the form of arod and has a hexagonal cross section, that is to say is formed like aregular hexagon.

The decoupling element 17 or 17 a formed in this way is conductivelyconnected at its base 21 to the reflector 5, for example beingelectrically conductively connected or capacitively connected to it.

The length of the element in the form of a rod, that is to say itsextent direction parallel to the propagation direction of theelectromagnetic waves of the antenna 1 formed in this way, that is tosay at right angles to the reflector 5, is preferably 0.05 times thewavelength to the wavelength of the antenna frequency band to betransmitted.

The diameter of the element in the form of a rod can likewise differwithin wide ranges, and is preferably approximately 0.01 to 0.2 timesthe wavelengths to be transmitted.

FIG. 2 will be used to show that a corresponding decoupling element 17,17 a can be provided between two radiating elements which are differentto those shown in FIG. 1. FIG. 2 in each case shows two dipole radiatingelements, which are each seated in pairs, aligned parallel, above andbelow the decoupling element. FIG. 2 shows a side view according to thearrow 2, relating to the exemplary embodiment shown in FIG. 1b.

The exemplary embodiment as illustrated in FIG. 3 and the further FIGS.3a to 3 c shows an antenna 1 which comprises two dipole radiatingelements joined together to form a cruciform dipole 3 b. A correspondingdecoupling element 17, 17 a is in each case arranged lying on an anglebisector 27 of the dipole radiating elements, which are arranged in acruciform shape in plan view, in the region of the cruciform dipole 3 b.This is thus a dual-polarized antenna arrangement with a cruciformdipole, in which case it is particularly surprising that the decouplingprinciple operates just with a cruciform dipole such as this. As isknown in principle in the case of cruciform dipoles (or, for example,dipole squares), two separate inputs are thus used for actuation,between which decoupling (or isolation) is measurable, in which case theuse of the decoupling device according to the invention can in this waybe verified. In this case, it is furthermore surprising that theprinciple of the decoupling elements according to the invention alsooperates when an asymmetric arrangement is used, that is to say, forexample in FIGS. 3 to 3 c, only one of the two decoupling elements isused.

The exemplary embodiment in FIG. 4 shows a plan view of a dipole square3 c at an appropriate distance in front of a reflector 5, with twodecoupling elements 17, 17 a being shown lying on an angle bisector 27in the region of the cruciform dipole 3 c, and each lying in a regionbetween the corner points 29 of the dipole square and the center point31 of the dipole square.

The exemplary embodiment in FIG. 5 shows two radiating element devicesarranged vertically one above the other, in the form of two cruciformradiating elements 36 in front of a vertically running reflector 5, witha decoupling element 17, 17 a according to the invention being showncentrally on the vertical fitting line or connecting line 11, andlikewise once again extending parallel to the propagation direction ofthe electromagnetic waves of the radiating elements, in other words atright angles to the plane of the reflector 5.

In the exemplary embodiment shown in FIG. 6, two dipole squares 3, 3 c,which are illustrated with reference to FIG. 4, are arranged in thevertical gap along a vertical connecting axis 11 in front of a reflector5, to be precise in each case with two decoupling elements 17, 17 a,located in a corresponding manner within the dipole square, andexplained with reference to FIG. 4. In addition, a fifth decouplingelement, which is in the form of a rod and is seated at right angles tothe reflector 5, is shown, along the vertical connecting line 11 in theillustrated exemplary embodiment, centrally between the two cornerpoints 35, which point toward one another, of the dipole squares 3 cformed in this way.

The fundamental design of the antenna device, and the use ofcorresponding decoupling elements 17, 17 a has been described forvarious antenna types. A number of further modifications of antennas,that is to say in particular other antenna types and the design andarrangement of different radiating elements are also feasible here, asrequired, in which all of the explained decoupling elements 17, 17 a canbe used.

In contrast to the illustrated exemplary embodiments, the decouplingelements 17, 17 a may also be shaped differently within wide ranges,and, in particular, they may also be provided with a different crosssection. The cross section of the decoupling elements 17, 17 a may, forexample, be n-polygonal, round, elliptical, with partially convex andconcave successive circumferential sections, or else may be designed insome other way, with the entire longitudinal extent of the decouplingelement 17, 17 a formed in this way, or its extent component at rightangles to the reflector 5 and/or parallel to the propagation directionof the electromagnetic waves of the antenna 1 being of a size which islarger than the cross-sectional size in any desired transverse directionparallel to the plane of the reflector 5. The cross-sectional shapetransversely with respect to the extent direction or parallel to thereflector 5 may thus vary over the length of the decoupling element 17,17 a not only from its extent size, but also from that shape. Inparticular, at the end of the decoupling element 17, 17 a located at thetop, that is to say opposite its base 21 which is seated on thereflector 5, further structural elements may also be provided, forexample conical or spherical fixtures, or asymmetric attachments,attachments in the form of bars, etc. with these attachments having asize in the direction parallel to the reflector 5 or transversely withrespect to the propagation direction of the electromagnetic waves whichis shorter than the extent component in the propagation direction of theelectromagnetic waves, that is to say at right angles to the reflector5.

The main extent direction 25 (FIG. 1a) of the decoupling element 17according to the invention is thus provided in an angle range of morethan 45° with respect to the plane of the reflector 5 up to preferably90°, that is to say running at right angles to the plane of thereflector 5.

Further variation options with regard to the decoupling elements 17 areshown in FIG. 7. FIG. 7 in this case shows a cross-sectionalillustration of the reflector plane 5, and of a decoupling element 17which is seated on it and which, as explained, may also be arrangedobliquely, that is to say not at right angles to the plane of thereflector plate 5. The angle a, that is to say the angle α formed by theperpendicular 41 to the plane of the reflector 5 with respect to theextent direction 43 of the decoupling element 17, is in this case lessthan 45°, preferably less than 30° or 150, and preferably just 0°. Thenormal 41 to the plane of the reflector 5 in this case corresponds,considering the far field, to the propagation direction of theelectromagnetic waves.

FIG. 8 shows that the decoupling element may also have differentcross-sectional shapes and sizes along its longitudinal extent.

FIG. 9 shows that fixtures or attachments 45 can be formed on thecoupling element, in particular at the upper end of the decouplingelement 17, which also project beyond the external size of that part ofthe decoupling element 17 which is located underneath. FIG. 9 shows, forexample, a spherical fixture.

In contrast, FIG. 10 shows a short fixture 45 in the form of a rod,whose maximum transverse extent is, however, less than the total heightof the decoupling element 17.

Any desired further modifications are to this extent feasible within thescope of the idea of the invention.

What is claimed is:
 1. An antenna comprising: a reflector; at least onedual-polarized radiating element arranged in front of the reflector andexhibiting a main electromagnetic wave propagation direction, theelement having at least one associated passive conductive decouplingelement, the decoupling element having a longest extent in onedirection, thus defining its main extent direction, the main extentdirection of the decoupling element being at least one of (a) parallelto the main propagation direction of the electromagnetic wave, whenconsidered in the far field, or (b) at right angles to the plane of thereflector or (c) includes an angle (α), which is less than 45°, whenconsidered in the far field, with at least one of (1) the mainpropagation direction of the electromagnetic wave, and (2) with aperpendicular to the plane of the reflectors.
 2. The antenna as claimedin claim 1, wherein the decoupling element has a base which iselectrically conductively connected to the reflectors.
 3. The antenna asclaimed in claim 1, wherein the decoupling element has a base which iscapacitively connected to the reflector.
 4. The antenna as claimed inclaim 1, wherein the length of the decoupling element or the projectionof the length of the decoupling element onto the main propagationdirection of the electromagnetic wave which is produced when consideredin the far field, or the perpendicular to the plane of the reflector isgreater than 0.05 times the wavelength of the electromagnetic wavestransmitted of received via the radiating elements.
 5. The antenna asclaimed in claim 1, wherein the extent length of the decoupling elementor its component in the propagation direction of the electromagneticwaves, when considered in the far field, or at right angles to the planeof the reflector is less than the wavelength of the electromagneticwaves transmitted or received via the radiating elements .
 6. Theantenna as claimed in claim 1, wherein the thickness of the decouplingelement is greater than 0.01 times the operating wavelength.
 7. Theantenna as claimed in claim 1, wherein the thickness of the decouplingelement is less than 0.2 times the operating wavelength.
 8. The antennaas claimed in claim 1, wherein the cross section transversely withrespect to the extent direction of the decoupling element isn-polygonal, round, elliptical or irregular.
 9. The antenna as claimedin claim 1, wherein the angle (α) between the extent direction in thelongitudinal direction of the decoupling element and the mainpropagation direction of the electromagnetic waves, which is producedwhen considered in the far field, or the normal to the plane of thereflector is less than 30°, preferably less than 15°, and in particularis around 0°.
 10. The antenna as claimed in claim 1, wherein thedecoupling element has a base and is provided, in particular at an endopposite the base, with an attachment or fixture which projects beyondthe cross-sectional size of that section of the decoupling element whichis located underneath.
 11. The antenna as claimed in claim 10, whereinthe attachment or fixture is least one of (a) spherical, (b) polygonal,or (c) in the form of a rod.
 12. The antenna as claimed in claim 1,wherein the decoupling element is in the form of a rod, a strip or awaveguide.
 13. The antenna as claimed in claim 1, wherein the at leasttwo radiating elements are provided, and in that the at least onedecoupling element is arranged between two adjacent radiating elements.14. The antenna as claimed in claim 13, wherein the at least onedecoupling element is arranged on the connection line (11) between twoadjacent radiating elements, preferably centrally between them.
 15. Theantenna as claimed in claim 1, wherein, in the case of a cruciformdipole, at least one, and preferably at least two, decoupling elementsare arranged in the region of the cruciform dipole.
 16. The antenna asclaimed in claim 1, wherein, in the case of a dipole square, at leastone, and preferably at least two, decoupling elements are arranged inthe region of the dipole square.
 17. The antenna as claimed in claim 15,wherein the at least one decoupling elements is arranged on an anglebisector.
 18. The antenna as claimed in claim 15, wherein the at leastone, and preferably the at least two, decoupling element is arranged onthe angle bisector between the center point of the radiating element andin front of its outer boundary.
 19. The antenna as claimed in claim 1,wherein the radiating elements comprise dipole radiating elements fortransmitting vertical polarizations, horizontal polarizations, ororthogonal polarizations.
 20. The antenna as claimed in claim 1, whereinthe antenna including the at least one coupling element, is asymmetric.21. The antenna as claimed in claim 1, wherein further including atleast two separate inputs that are measurably decoupled from oneanother.
 22. The antenna as claimed in claim 1, wherein including pluralidentically-designed decoupling elements.
 23. The antenna as claimed inclaim 1, wherein a number of decoupling elements are provided, saidnumber of decoupling elements being designed differently.
 24. An antennacomprising: a planar reflector; at least one dual-polarized radiatingelement disposed in front of the reflector, said radiating elementexhibiting a main electromagnetic propagation direction; and at leastone passive conducting decoupling element disposed on and coupled tosaid reflector, said decoupling element comprising a rod having alongitudinal extent and a width extent, the longitudinal extent beinggreater than the width extent, the angle between the rod's longitudinalextent and a perpendicular to the plane of the planar reflector beingless than 45 degrees when considered in the far field.
 25. An antennacomprising: a planar reflector; at least one dual-polarized radiatingelement disposed in front of the reflector, said radiating elementexhibiting a main electromagnetic propagation direction; and at leastone passive conducting decoupling element disposed on and coupled tosaid reflector, said decoupling element comprising a rod having alongitudinal extent and a width extent, the longitudinal extent beinggreater than the width extent, the angle between the rod's longitudinalextent and the main propagation direction exhibited by the radiatingelement being less than 45 degrees when considered in the far field. 26.An antenna comprising: a planar reflector, at least one dual-polarizedradiating element disposed in front of the reflector, said radiatingelement exhibiting a main electromagnetic propagation direction; and atleast one passive conducting decoupling element disposed on and coupledto said reflector, said decoupling element comprising a rod having alongitudinal extent and a width extent, the longitudinal extent beinggreater than the width extent, the rod's longitudinal extent beingparallel to said main propagation direction, when considered in the farfield.
 27. An antenna comprising: a planar reflector; at least onedual-polarized radiating element disposed in front of the reflector,said radiating element exhibiting a main electromagnetic propagationdirection; and at least one passive conducting decoupling elementdisposed on and coupled to said reflector, said decoupling elementcomprising a rod having a longitudinal extent and a width extent, thelongitudinal extent being greater than the width extent, the rod'slongitudinal extent being at right angles to the plane of the reflector.